Nanotube field emission display comprises an emitting image pixel array formed of conductive paste being screen printed on a substrate having patterned silver cathode thereon. The conductive paste consisting of carbon nanotube (CNT), organic bonding agent, and silver powder. The CNT has a shape of about 5-100 nm in diameter and 1000-3000 nm in length. The principle of field emission is in terms of electric field accelerating cold electrons which are emitted from the tip of each CNT through vacuum space and bombards anode which is an indium tin oxide (ITO) substrate having phosphor pixel to generate fluorescence. By contrast to conventional cathode ray tube, it is in terms of a principle of emitted electrons thermoionically from a tungsten wire, the field emission molding has a quite different way.
Field emission display can have a benefit of very thin electron gun of only about 0.2 mm in thickness. In addition, the size of planar area can have very flexible, it can be very small such as 1 cm2 and can as large as several hundred centimeter square. The CNT-FED (CNT-field emission display) is thus a prominence for an ultra thin flat panel display. For a display, the stability and long life reliability are fundamental characteristics. However, as high as 10-100 mA/cm2 in current density is a minimum criteria and the most critical characteristic for generating sufficient brightness and uniformity for a display. To approach such current density, the lower intensity electrical field is preferred. Preferably, it should be lower than 25 V/μm.
The electric property (current density vs. intensity of electric field) is predetermined by a number of exposed CNT. Thereafter, to improve the fluorescence efficiency, a three-electrode structure is a common control switch for field emitting display. The principle of the three-electrode structure of CNT-FED is by means of anode to provide energy for electrons, a cathode as an electron emitting source, and a gate provided for accelerating the outgoing electrons.
Currently to form a CNT field emitting source, a CNT paste mixed with CNT and organic bonding agent are provided. A method of screen print is then used to coat the CNT paste on the patterned silver electrodes through the openings of the three-electrode structure, Whereas, a prerequisite of using screen print technique is that it should have appropriate mounting areas provided for CNT paste so that the CNT paste can accurately paste on the targets. However, a typical size of opening 2 for forming a CNT-FED pixel of three-electrode structure is about 80 μm in width and 30 μm in depth, as is shown in FIG. 1. The sidewall of opening is readily adhered with some CNT paste, as a result, the cathode electrode may be short to the gate electrode 1. Even worse, the CNT paste does not adhere to the cathode line anyway.
Another technique by the conventional method includes the steps of: coating a CNT layer on the silver cathodes; forming a dielectric layer on the CNT layer, forming gate lines on the dielectric layer and then patterning the dielectric layer so as to expose desired CNT. The disadvantages of this technique include: the openings for pixel are difficult to etch due to too deep of the opening and contamination generated on the CNT during etching step.
Still another technique of the traditional method is the emitting source formed by coating a photo-sensitive CNT paste and then performing a lithographic step to form desired CNT emitting sources. The deficient of this technique includes incompletely exposure of photo-sensitive CNT paste on sidewall. After developing, some residues on the sidewall are often found. As a result, the gate electrode may be shorted to the cathode,
The forgoing prior arts do not provide an available method to solve aforementioned problems found in the fabricating process for the three-electrode CNT emitting source. Thus, an object of the present invention is to provide a method which solve above issues by simple processes, i.e. an imprint method.